Vision is one of the enduring puzzles of modern cognitive science and elucidating the mechanisms of visual object perception presents a particular challenge. Nothing in the reflected light that arrives at the retina contains direct information about the location, shape, size, or number of objects in view. Understanding how the brain processes visual stimuli to derive this information would be a major advance in visual science. Because birds are active and mobile, avian visual systems must resolve the same problems that have driven theoretical advances in human and machine vision research. Examining these issues in such small, non-mammalian systems adds substantially to the development of a unified general theory of vision. Using our well-developed psychophysical techniques based on discrimination learning, we propose to evaluate this problem by examining in how starlings and pigeons process visual stimuli in controlled analytical contexts. This will be the first parallel comparison of visual processing in two avian species. The overall objective of this application is to investigate and compare how these species solve central problems of visual cognition and object perception as related to the processing of illumination and shading, edge processing and figural grouping, and the recognition and classification of behavior and action. Our specific aims include: 1) equating our procedures for the comparative examination of visual processing in these species; 2) examining the processing of surface shading and its contributions to object and depth perception; 3) examining edge and figural grouping processes in shape perception; and 4) examining the mechanisms of visually-mediated action and movement recognition. The current project is a part of our long-term objective to understand the proximate psychological, computational and neural mechanisms by which different pattern recognition systems perceive, recognize, categorize, integrate, understand, and respond to complex visual information. The unique combination of visual power, small size, and different neural organization exemplified by birds offers a special scientific opportunity for better understanding this extremely important sensory modality and how it functions and is implemented across different classes of animals. This comparison will address whether there are only a few biologically plausible mechanisms for rapid visual processing of objects or whether there are multiple routes to functional vision in highly mobile organisms. Because there is strong evolutionary pressure for highly efficient and rapid computation of visual information placed on the small, highly visual brain of birds, our results will contribute directly to the pracical development of treatments, corrective solutions or prostheses for humans with a variety of visual disorders and to the design of visual sensors for self-guided bio-mimetic robotic devices.